The prevalence and type of social noise exposure in young adults in England.

There have been several recent reports on the potential risk to hearing from various types of social noise exposure. However, there are few population-based data to substantiate a case for concern. During the last 10-20 years use of personal cassette players (PCPs) has become very much more prevalent, and sound levels in public nightclubs and discotheques are reported to have increased.

Cinemas - do they pose a risk to hearing?

Noise measurements were made in cinemas during the showing of four films, to establish whether the noise levels from films might pose a risk of damage to hearing. The L(Aeq) levels for the full playing time of each film were all below 80 dB(A). Noise levels did sometimes exceed 90 dB(A) but this was never for more than a total of two minutes, and was usually for only a few seconds.

The contribution of social noise to tinnitus in young people - a preliminary report.

In our study of the Hearing in Young Adults (HIYA) aged 18-25 years, there appeared to be little effect of social noise on hearing thresholds (Smith et al. 1998). There was however, a threefold increase in the reports of tinnitus in those subjects with significant social noise exposure (>/=97 dB NIL).

Health-service costs of pediatric cochlear implantation: multi-center analysis.

Objective: Pediatric cochlear implantation (CI) entails surgery followed by lifetime maintenance, and hence incurs both initial and ongoing costs. Previous assessments of these costs were either undertaken early in the evolution of services, or were based on single hospitals, or estimated costs largely from hospital charges. The aim was to overcome these limitations by conducting a multi-center evaluation of the costs of providing unilateral CI to children in the United Kingdom (UK).

A method for determining venous contribution to BOLD contrast sensory activation.

While BOLD contrast reflects hemodynamic changes within capillaries serving neural tissue, it also has a venous component. Studies that have determined the relation of large blood vessels to the activation map indicate that veins are the source of the largest response, and the most delayed in time. It would be informative if the location of these large veins could be extracted from the properties of the functional responses, since vessels are not visible in BOLD contrast images.

Auditory neuroscience: the salience of looming sounds.

Sounds that move towards us have a greater biological salience than those that move away. Recent studies in human and non-human primates have demonstrated a perceptual and behavioural priority for such looming sounds that is also reflected in an asymmetric pattern of cortical activation.

Relationships between human auditory cortical structure and function.

The human auditory cortex comprises multiple areas, largely distributed across the supratemporal plane, but the precise number and configuration of auditory areas and their functional significance have not yet been clearly established. In this paper, we discuss recent research concerning architectonic and functional organisation within the human auditory cortex, as well as architectonic and neurophysiological studies in non-human species, which can provide a broad conceptual framework for interpreting functional specialisation in humans. We review the pattern in human auditory cortex of the functional responses to various acoustic cues, such as frequency, pitch, sound level, temporal variation, motion and spatial location, and we discuss their correspondence to what is known about the organisation of the auditory cortex in other primates.

The roles of unconventional myosins in hearing and deafness.

The proper expression and function of several unconventional myosins are necessary for inner-ear function. Mutations in MYO7A and MYO15 cause deafness in humans, and mice. Whereas mutations in Myo6 cause inner-ear abnormalities in mice, as yet no human deafness has been found to the result of mutations in MYO6.

A novel stereocilia defect in sensory hair cells of the deaf mouse mutant Tasmanian devil.

Stereocilia are specialized actin-filled, finger-like processes arrayed in rows of graded heights to form a crescent or W-shape on the apical surface of sensory hair cells. The stereocilia are deflected by the vibration of sound, which opens transduction channels and allows an influx of ions to depolarize the hair cell, in turn triggering synaptic activity. The specialized morphology and organization of the stereocilia bundle is crucial in the process of sensory transduction in the inner ear.

Phase-locked responses to pure tones in the primary auditory cortex.

At the level of the brainstem, precise temporal information is essential for some aspects of binaural processing, while at the level of the cortex, rate and place mechanisms for neural coding seem to predominate. However, we now show that precise timing of steady-state responses to pure tones occurs in the primary auditory cortex (AI). Recordings were made from 163 multi-units in guinea pig AI.

Electronic aids to hearing.

Despite many scientific developments in the biology of hearing, there remain no wide-spread medical or surgical interventions for listeners with sensorineural hearing impairments. In addition to describing technical advances, this chapter identifies important aspects of candidature for hearing aids and some issues of service delivery.

Microelectrode and neuroimaging studies of central auditory function.

Imaging studies in humans are revealing parallels with the functional organisation of the auditory brain discovered in microelectrode studies in animals: the rate of amplitude modulation generating the strongest response declines systematically from the lower brain stem to the cortex; an increase in sound level induces a higher level and a greater extent of activity; spectra are represented tonotopically in multiple cortical areas. There are also differences: evidence of organisation reflecting the sound level of the stimulus is absent in animals, but has been found in humans. Additionally, imaging has revealed functional specialisations which have not (yet) been located in animals: areas that respond more strongly to sounds with stronger pitches and to sounds that move in space.

Heschl's gyrus is more sensitive to tone level than non-primary auditory cortex.

Previous neuroimaging studies generally demonstrate a growth in the cortical response with an increase in sound level. However, the details of the shape and topographic location of such growth remain largely unknown. One limiting methodological factor has been the relatively sparse sampling of sound intensities.

Elongation of hair cell stereocilia is defective in the mouse mutant whirler.

The recessive mouse mutant whirler (wi) shows no response to sound and exhibits circling and head-tossing behaviour, indicative of both auditory and vestibular dysfunction. The wi mutation maps genetically to mouse chromosome 4. We examined the organ of Corti of whirler mutants to explore the possibility that the wi mutation affects sensory hair cells.

Stereocilia defects in waltzer (Cdh23), shaker1 (Myo7a) and double waltzer/shaker1 mutant mice.

Mutations in myosin VIIa (Myo7a) and cadherin 23 (Cdh23) cause deafness in shaker1 (sh1) and waltzer (v) mouse mutants respectively. In humans, mutations in these genes cause Usher's syndrome type 1B and D respectively, as well as certain forms of non-syndromic deafness. Examination of the organ of Corti from shaker1 and waltzer mice has shown that these genes are required for the proper organisation of hair cell stereocilia.

Spectrotemporal receptive field properties of single units in the primary, dorsocaudal and ventrorostral auditory cortex of the guinea pig.

We report the spectrotemporal response properties of single units in the primary (A1) and dorsocaudal (DC) fields, and the ventrorostral belt of the urethane-anaesthetised guinea pig auditory cortex. Using reverse correlation analysis, spectrotemporal receptive fields (STRFs) were constructed and subsequently classified according to a novel qualitative scheme that was based on the duration and bandwidth of excitatory and inhibitory regions within the STRF. The STRFs of units in both A1 and DC showed either broad-band (> or = 1 octave) or narrow-band (< 1 octave) excitatory and inhibitory regions occurring either alone or together.

Temporal nonlinearity revealed by transient evoked otoacoustic emissions recorded to trains of multiple clicks.

A series of detailed experiments is described that investigates how a transient evoked otoacoustic emission (TEOAE) recorded to one-click stimulus is affected by the presence of a variable number of preceding clicks presented over a range of interclick intervals (ICIs). Part of the rationale was to determine if the resulting nonlinear temporal interactions could help explain the amplitude reduction seen when TEOAEs are recorded at very high click rates, as when using maximum length sequence stimulation. Amongst the findings was that the presence of a preceding train of clicks could either suppress or enhance emission amplitude, depending on the number of clicks in the train and the ICI.

Heritability of symptom domains in otitis media: a longitudinal study of 1,373 twin pairs.

Research on risk factors and pathogenesis of otitis media has emphasized the environment, but previous twin studies suggest a strong genetic component. In those studies, no attempt was made to differentiate the role of initial acute infection from the chronic airway blockage that frequently accompanies persistent effusion. The authors estimated genetic and environmental determination of both of these aspects of otitis media histories at three time points.

Early development and degeneration of vestibular hair cells in bronx waltzer mutant mice.

In bronx waltzer mouse mutants, inner hair cells die at an early stage in their development, from around 17.5 days of gestation onwards. In contrast, outer hair cells appear to develop normally.

ENU mutagenesis reveals a highly mutable locus on mouse Chromosome 4 that affects ear morphogenesis.

Chemical mutagenesis followed by screening for abnormal phenotypes in the mouse holds much promise as a method for revealing gene function. This method is particularly well-suited for discovering genes involved in hearing or balance function, as these defects are relatively easy to screen for in the mouse. We report here the inner ear abnormalities and genetic localization of seven new dominant mutations created by ENU mutagenesis.

Histochemical identification of cortical areas in the auditory region of the human brain.

Despite numerous studies stretching over the last 100 years there is still no general agreement on the number of auditory areas in the human cortex or even how to define them by histological methods. Full definition of these areas will require a combination of functional and histological methods but, by using six complementary histological methods, of which most have been used in the monkey, we provide a clearer description of these areas. The primary auditory area was located on the posteromedial two-thirds of the first transverse temporal (Heschl's) gyrus and was distinguished by a dense band of cytochrome oxidase activity in layer IV and the base of layer III, as well as a relatively thick, pale layer V and VI.

Interconnections of auditory areas in the guinea pig neocortex.

By studying the efferent projections of five auditory areas in the guinea pig cortex, we sought evidence that the larger fields can be divided into subareas based on unique patterns of cortical connections. Small extracellular injections of biocytin were made in combination with evoked potential mapping or single-unit analysis and histochemical determination of cortical landmarks. The two core fields, primary (AI) and dorsocaudal (DC), are partially surrounded by six adjacent belt areas, leaving two gaps: one at the rostral edge of AI and the other at the dorsal edge.

Use of vocalic information in the identification of /s/ and /sh/ by children with cochlear implants.

Objective: When a syllable such as "sea" or "she" is spoken, listeners with normal hearing extract evidence of the fricative consonant from both the fricative noise and the following vocalic segment. If the fricative noise is made ambiguous, listeners may still perceive "s" or "sh" categorically, depending on information in the vocalic segment. Do children whose auditory experience comes from electrical stimulation also display this effect, in which a subsequent segment of speech disambiguates an earlier segment?

Design: Unambiguous vowels were appended to ambiguous fricative noises to form tokens of the words "she," "sea," "shoe," and "Sue.